/** Draw Rorentz Attractor
  where differential equations are
  dX
 ---- = - \sigma X + \sigma Y
  dt

  dY
 ---- = - X Z + r X - Y
  dt

  dY
 ---- =  XY - b Z
  dt
\sigma = 10, b = 8/3, r = 28
\sigma は プラントル定数、流体の拡散係数と熱伝導係数の比
r, b は 容器の形や流体の性質に関するパラメータ

文献「カオスとフラクタル ---非線形の不思議---」山口昌哉、ブルーバックス
**/
import java.awt.*;
import java.applet.*;
import java.util.Random;

public class Rorentz extends Applet {
  RorentzGraph drawingCanvas;
  Panel PrmPanel, CntrlPanel, InputPanel;

  TextField TFsigma, TFr, TFb, TFinit;
  double sigma=10.0, b=8.0/3.0, r=28.0;

  public void init() {
    setLayout(new BorderLayout());
    PrmPanel = new Panel();
    PrmPanel.setLayout(new FlowLayout());
    PrmPanel.add(new Label("sigma=", Label.RIGHT));
    PrmPanel.add(TFsigma = new TextField(String.valueOf(sigma), 4));
    PrmPanel.add(new Label(" b=", Label.RIGHT));
    PrmPanel.add(TFb = new TextField(String.valueOf(b), 4));
    PrmPanel.add(new Label(" r=", Label.RIGHT));
    PrmPanel.add(TFr = new TextField(String.valueOf(r), 4));
    CntrlPanel = new Panel();
    CntrlPanel.setLayout(new FlowLayout());
    CntrlPanel.add(new Button("Start"));
    CntrlPanel.add(new Button("Stop"));
    CntrlPanel.add(new Button("Clear"));
    InputPanel = new Panel();
    InputPanel.setLayout(new GridLayout(2,1));
    InputPanel.add(PrmPanel);
    InputPanel.add(CntrlPanel);
    add("Center", drawingCanvas = new RorentzGraph(sigma, b, r));
    add("South",  InputPanel);
    drawingCanvas.start();
  }

  public boolean action(Event ev, Object arg) {
    if (ev.target instanceof TextField) {
      sigma = Float.valueOf(TFsigma.getText().trim()).floatValue();
      b     = Float.valueOf(TFb.getText().trim()).floatValue();
      r     = Float.valueOf(TFr.getText().trim()).floatValue();
      drawingCanvas.setparam(sigma, b, r);
      return true;
    } else if (ev.target instanceof Button){
      String l = ((Button)ev.target).getLabel();
      if ( "Start".equals(l) ){
	drawingCanvas.start();
      } else if ( "Stop".equals(l) ){
	drawingCanvas.stop();
      } else if ( "Clear".equals(l) ){
	drawingCanvas.clear();
      }
      return true;
    } else 
      return true;
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      stop();
      destroy();
      System.exit(0);
      return true;
    } else {
      return super.handleEvent(e);
    }
  }

  public static void main(String args[]) {
    PFrame f = new PFrame("Rorentz Attractor");
    Rorentz rorentz = new Rorentz();

    rorentz.init();
    rorentz.start();

    f.add("Center", rorentz);
    f.resize(420, 500);
    f.show();
  }
}

class PFrame extends Frame {
  PFrame(String title) {
    super(title);
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      dispose();
      System.exit(0);
    }
    return false;
  }
}
    
class RorentzGraph extends Canvas implements Runnable {
  static Point A = new Point(0,0), B = new Point(0,0);
  static Point O = new Point(0,0);
  static Point U = new Point(8,8);
  int Height, Width;

  static double sigma = 10.0, b = 8.0/3.0, r = 28.0;
  static double x, y, z, dx, dy, dz, t, dt;
  Random rnd;
  Thread th;
  boolean clrflg = false;

  public void init() {
    if (th == null){
      th = new Thread(this);
    }
  }

  public void start() {
    if (th == null) {
      th = new Thread(this);
      th.start();
    } else 
      th.resume();
  }

  public void stop() {
    if (th != null) {
      th.suspend();
    }
  }

  public void run() {
    while (true) {
      try {
	Thread.sleep(100);
      } catch (InterruptedException e) {
	break;
      }
      repaint();
    }
  }

  public void update(Graphics g) {
    paint(g);
  }

  public void clear() {
    setForeground(Color.black);
    this.getGraphics().fillRect(0, 0, Width, Height);
    setForeground(Color.red);
  }

  RorentzGraph(double sigma, double b, double r){
    rnd = new Random();
    x = rnd.nextDouble();
    y = rnd.nextDouble();
    z = rnd.nextDouble();
    t = 0.0;
    this.sigma = sigma;
    this.b = b;
    this.r = r;
    aw2px(A, x, y);
    setBackground(Color.black);
    setForeground(Color.red);
    repaint();
  }

  public void setparam(double sigma, double b, double r){
    this.sigma = sigma;
    this.b = b;
    this.r = r;
  }

  public void aw2px(Point t, double x, double y){
    t.x = (int)(   x * (double)U.x + (double)O.x );
    t.y = (int)( - y * (double)U.y + (double)O.y );
  }

  public void draw_coordinate(Graphics g) {
    g.setColor(Color.pink);
    for (int i = -10; i <= 10; i++) {
      aw2px(A, -10,i);  aw2px(B,  10,i);
      g.drawLine(A.x, A.y, B.x, B.y);
    }
    for (int i = -10; i <= 10; i++) {
      aw2px(A, i,-10);  aw2px(B, i, 10);
      g.drawLine(A.x, A.y, B.x, B.y);
    }

    g.setColor(Color.black);
    aw2px(A,0,-10); aw2px(B,0, 10);
    g.drawLine(A.x, A.y, B.x, B.y);
    aw2px(A,-10,0); aw2px(B,10,0);
    g.drawLine(A.x, A.y, B.x, B.y);
  }

  public void paint(Graphics g) {
    Height = size().height;
    Width  = size().width;
    O.x = Height / 2;
    O.y = Width  / 2;

    g.setColor(Color.red);

    double tt = t + 1.0, dt = 0.01;
    while ( t <= tt ) {
      dx = (- sigma * x + sigma * y) * dt;
      dy = (-x * z + r * x - y) * dt;
      dz = (x * y - b * z) * dt;

      aw2px(A, x, y);
      x += dx;
      y += dy;
      z += dz;
      aw2px(B, x, y);
      g.drawLine(A.x, A.y, B.x, B.y);
      t += dt;
    }
  }
}